The numbers of women who receive adjuvant chemotherapy for breast cancer could be reduced by 30 to 40% if the results of a new molecular study are put into practice.

Dr Laura van 't Veer from the Netherlands Cancer Institute told a news briefing at the 3rd European Breast Cancer Conference that micro array technology* can help predict which breast cancers will metastasise (spread) and which will not.

Dr van 't Veer said her team had now validated data on a series of 73 patients diagnosed with lymph-node negative breast cancer under the age of 55, updating a report that appeared in the journal Nature in January.

"We have confirmed that we can predict with 90% certainty that a patient will remain free of breast cancer for at least five years.

"We may be able to reduce the use of chemotherapy in this group of patients by 30 to 40% if we use this information when planning their treatment."

The study on the 73 patients demonstrated that the outcome of the disease was related to the pattern of gene expression in the tumour. The tumour tissue of the patients whose breast cancer had metatasised within five years had a different profile - one in which the genes involved in the regulation of the cell cycle, cancer invasion, metastasis and angiogenesis (formation of blood vessels) were over-expressed. Dr van 't Veer said that the research team were now carrying out micro arrays on a larger series of breast cancer samples to be able to apply micro array profiling to young breast cancer patients in general.

"Cancer patients younger than 55 whose cancer has not spread to the lymph nodes are not only treated by surgery and radiotherapy but also generally receive adjuvant treatment (chemotherapy and/or hormone therapy given after surgery). This type of treatment substantially reduces the chance of the cancer spreading. But chemotherapy especially has serious side effects and even without the treatment 70 to 80% of this group of patients would remain disease-free. As we don't have a way to select those patients who are at highest risk there is no way to prevent overtreatment, unless we are willing to accept that overall mortality will increase if we don't give adjuvant treatment. Our findings provide the potential to resolve the dilemma."

*Micro array studies involve using a DNA microchip bearing thousands of known single-stranded gene fragments on its surface and incubating it with RNA from tissue samples. By seeing which gene fragments the RNA is attracted to, it is possible to tell which genes are active in the tissue samples.